The present invention relates to positioners for positioning objects, and more particularly to a deformable positioning stage.
Assembly of optic-electronic devices requires precision alignment of optical fibers with lasers or sensors and then bonding. A worker looking through a microscope at the end of a fiber conventionally executes this precision alignment and bonding process.
The alignment and bonding process can take as little as five minutes. However, if there is a misalignment of the fiber ends, this process can take as long as forty-five minutes to an hour. Misalignment often occurs because the fibers are subject to other than pure linear movement during the alignment process. Accordingly, a need exists for an improved alignment process which will reduce, if not eliminate, misalignment of a fiber end.
It is likely that in the next ten years the use of opto-electronic devices will spread to automobiles and every phone and computer manufactured in the United States, resulting in an estimated volume of 25 million units produced per year. Conventional assembly of opto-electronic devices can, as discussed above, require substantial worker time and therefore be quite costly. Accordingly, a need exists for a way to assemble opto-electronic devices which would require less worker effort and hence reduce the cost of assembly.
In other fields, delicate precision micrometer, sub-micrometer and nanometer assembly or positioning is also required. Such fields include medicine, biotechnology and electronic manufacturing. For example, individual atoms, molecules or nano-particles may be combined or separated to build materials and devices exhibiting desirable properties. Positioning devices currently available do not provide the precision and range of motion required in these and other technological fields. Accordingly, an improved technique is required for performing precision movement, often referred to as fine movement, at each of the micrometer, sub-micrometer and nanometer levels.
A planar biaxial micropositioning stage, which includes a deformable structure micro-positioning stage and which utilizes two nested cantilever flexure mechanisms facilitating movement of the stage in each of the X and Y axes has been proposed for use in precision manufacturing. A force can be applied to the proposed structure by an actuator to move the stage along the intended axis of movement. The actuator placement in this positioner is perpendicular to the axis of movement of the stage. However, the resulting movement in each of the X and Y directions is not purely linear. Rather, the proposed structure introduces a yaw which is unacceptable for precision manufacturing applications. This yaw is often referred to as a rotational cross talk error.
Known prior art positioning devices can not eliminate rotational cross talk unless additional actuators are included in the device to apply counterbalancing rotation and thereby ensure pure linear movement. These actuators add undesirable complexity and costs to the devices. Additionally, complex control algorithms must be developed and used to operate multiple actuators in concert to compensate for the cross talk.
In the proposed micro-positioning stage discussed above, as well as other proposed stages, the rotational cross talk error is inherent in the design. That is, applying a force intended to move a stage in one direction necessarily produces an unintended rotation. Accordingly, a need exists for a micro-positioner which does not impart rotational cross talk error into intended linear movement.
Control of conventional micro-positioners is performed through the use of feedback loops. At least one sensor is required to measure movement of a stage. Conventional deformable structure micro-positioners use sensors which are typically located at a position which results in inaccurate measurement of the true stage displacement. This inaccuracy due to sensor placement is commonly referred to as Abbe effect. Accordingly, a positioner is required which provides more accurate sensing.
Conventional deformable structure micro-positioners require that the actuator used to impart a force upon a movable stage be attached to the movable stage with an epoxy compound, or some other adhesive. These attachments impart a loss of force into the system. For example, when a force is applied to an epoxy connection between the actuator and the moving stage, the epoxy compresses, resulting in up to a 60 percent loss in applied force. Hence, an improved technique is required to attach an actuator to a movable stage to reduce the loss of force.
Using an epoxy or screws for the coupling, it is also difficult to obtain a pure parallel alignment of the actuator and the moving stage. Unparallel alignment results in a loss of force in the system. Furthermore, misalignment between the components may produce damaging stresses on the actuator. Accordingly, an improved coupling is required to achieve a parallel attachment between the coupling and an actuator.
Epoxy couplings are also subject to maintenance difficulties and durability limits. To remove an actuator from a deformable structure micro-positioner with epoxy couplings, the epoxy coupling must be cut using a machine tool. The two surfaces exposed by the cutting must be cleaned before they are reattached. This cutting and cleaning process may damage both the actuator and the deformable structure micro-positioner. Accordingly, a need exists for an improved technique of attaching and removing an actuator from a micro-positioner which eliminates the potentially damaging cutting and cleaning process.
Conventional deformable structure micro-positioners can be subjected to forces which may damage the individual components of a positioner. These forces may include inadvertent contact with the movable stage portion of the positioner or over-actuation of a drive used to move the movable stage. Accordingly, a need exists for a deformable structure micro-positioner which can better withstand damaging forces.
Deformable structure micro-positioners with one and two-degrees of freedom are well known. Six-degree of freedom positioners in the macro-scale are common. One type of six-degree of freedom positioner is often referred to as a Stewart platform. One familiar use of Stewart platforms is in aircraft simulators. However, a practical adaptation of macro-scale Stewart platforms to the micro-scale using a deformable structure platform has not been previously achieved.
A Stewart platform utilizes six struts to support a platform. Historically, macro-scale Stewart platform devices place drives, e.g. actuators, in each of the struts to obtain movement of the platform. In the proposed micro-scale adaptations of Stewart platforms, actuators are also placed in the struts. However, actuators of the type typically used in micro-scale positioners do not have the required range of motion necessary for use in the struts of a micro-scale adapted Stewart platform. Hence, more expensive and much larger actuators must be used in the proposed micro-scale Stewart platforms.
The February 1994 issue of NASA Tech Briefs proposed a positioner, characterized as a minimanipulator, with six-degrees of freedom. The drives which produce movement of the platform include stepping motors and rotary actuators. Each of these drives are subject to sticktion and backlash. Hence, this manipulator is not capable of achieving fine movement, since none of the actuator configurations usable in this device can produce movement without some sticktion and/or backlash. Accordingly, a need exists for an improved six-degree of freedom positioner which is capable of providing fine movement in each of the six degrees of freedom.
The conventional process for manufacturing deformable structure micro-positioning devices is costly and time-consuming. Typically, each device must be individually machined from a separate piece of material. Additionally, six-degree of freedom micro-positioners require separate manufacturing and assembly steps for each of the individual positioners. Accordingly, a need exists for a manufacturing process to produce a plurality of deformable structure micro-positioning devices, including six-degree of freedom devices, which is less costly and time-consuming.
One object of the present invention is to provide an improved technique for fine precision object manipulation in manufacturing and assembly processes.
Another object of the present invention is to provide a micro-positioning stage with precision movement on at least one of the micrometer, sub-micrometer and nanometer levels.
Another object of the present invention is to provide a micro-positioning stage with pure linear movement along an intended linear axis of movement.
Another object of the present invention is to provide a six-degree of freedom positioning stage with precision movement on at least one of the micrometer, sub-micrometer and nanometer levels.
Additional objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to preferred embodiment(s), it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.
In accordance with the present invention, a positioning device is provided. The positioning device may be used to position many different types and sizes of objects. These objects can range from large objects, which are commonly referred to as macro-scale objects, to very small objects, which are often referred to as micro-scale objects. Some objects in the micro-scale are measured in micro-meters. However, smaller objects in the micro-scale are measured in sub-micrometers. And, extremely small objects in the micro-scale are measured in nanometers. Objects at the nano-level are smaller than those measured in sub-microns. Objects in this smallest scale can include individual atoms.
The device includes a movable platform where objects to be positioned are placed for positioning. A plurality of struts are attached to the movable platform and to a monolithic base. Each strut, sometimes referred to as an extension, is attached at one end to the movable platform, and at its other end to the monolithic base.
The monolithic base is formed of a single piece, e.g. a block, of material which moves each of the struts independently, which in turn move the movable platform.
Beneficially, each of the struts can be attached to the monolithic base by a respective flexure. Each of the struts may, if desired, also be attached to the movable platform by a respective flexure. Advantageously, the plurality of struts is a total of six struts. The six struts are beneficially attached symmetrically about the movable platform. That is, the points at which the struts are attached to the movable platform are disposed equal distances from one another on the movable platform.
In accordance with other aspects of the invention, at least one sensor senses movement of the movable platform, and/or a stop member limits movement of the movable platform.
In a particularly advantageous implementation of the invention, the monolithic base includes three positioning stages. Preferably, the stages are machined into the base by removing material from the base.
Each of the three positioning stages has a portion, preferably an equal portion, of the plurality of struts attached to it. That is, the ends of each respective portion of the struts are attached to an associated one of the positioning stages, preferably at the center of the positioning stage. The portion of the struts attached to a positioning stage moves as a result of movement of that positioning stage. The movable platform moves as a result of movement of one or more of the positioning stages. Thus, the movable platform is moved by moving one, two, or all three of the positioning stages.
Beneficially, each of the three positioning stages moves in two orthogonal directions. If desired, each of the three positioning stages can be positioned independent of the positioning of any of the other positioning stages.